epf81188ari240-4h Altera Corporation, epf81188ari240-4h Datasheet - Page 9

• Manufacturer Part Number: epf81188ari240-4h
• Description: Programmable Logic Device Family
• Manufacturer: Altera Corporation

Altera Corporation
Figure 4. FLEX 8000 Carry Chain Operation
Cascade Chain
With the cascade chain, the FLEX 8000 architecture can implement
functions that have a very wide fan-in. Adjacent LUTs can be used to
compute portions of the function in parallel; the cascade chain serially
connects the intermediate values. The cascade chain can use a logical AND
or logical OR (via De Morgan’s inversion) to connect the outputs of
adjacent LEs. Each additional LE provides four more inputs to the
effective width of a function, with a delay as low as 0.6 ns per LE.
a1
b1
a2
b2
a n
b n
Carry-In
FLEX 8000 Programmable Logic Device Family Data Sheet
Carry Chain
Carry Chain
Carry Chain
Carry
LUT
LUT
LUT
LU
Register
Register
Register
Register
LE n + 1
LE1
LE n
LE2
s1
s2
Carry-Out
s n
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